Table 22. — Intensity and periodicity of activity through the four passages into the food pen 
A 
Number 
Mean 
number of 
Mean percentage of the total activity 
Range high 
percent 
minus low 
percent 
Median date 
of days 
activity 
units per 
day 
North 
East 
South 
West 
Nov. 14-15, 1947 
13 
411 
39. 9 
18. 8 
18. 3 
22. 9 
21. 6 
Dec. 24-25, 1947 
11 
432 
40. 5 
19. 9 
14. 3 
25. 3 
26. 2 
Apr. 17-18, 1948 
15 
1, 539 
24. 4 
26. 0 
17. 3 
32. 4 
15. 1 
May 8-9, 1948 
13 
2, 057 
22. 8 
25. 2 
22. 2 
29. 8 
7.6 
Apr. 12-13, 1949 
4 
2, 941 
37. 0 
25. 1 
16. 9 
20. 9 
20. 1 
Mean 
32. 9 
23. 0 
17. 8 
26. 3 
B 
Median date 
Number 
of days 
Mean percentage of postmidnight activity 
Range high 
percent 
minus low 
percent 
Mean of 
all passages 
North 
East 
South 
West 
Nov. 14-15, 1917 
13 
37. 3 
45. 2 
34. 7 
35.0 
34. 2 
11.0 
Dec. 24-25, 1917 
11 
34. 8 
38. 6 
36. 9 
32. 4 
31. 1 
7. 5 
Apr. 17-18, 1948 
15 
43. 8 
44. 1 
45. 6 
39. 5 
45. 9 
6.4 
May 8-9, 1948 
13 
42. 4 
41. 7 
41. 8 
41. 6 
44. 3 
2. 7 
Apr. 12-13, 1949 
4 
38. 9 
44. 3 
40. 0 
30. 8 
40. 3 
13. 5 
Mean 
42. 8 
39. 8 
35. 9 
39. 1 
time their periods of activity and inactivity more 
or less in unison. The coincidence of activity 
despite differences in age and place of harborage 
augers for the influence of a social influence by 
communication upon inception of activity. Ter- 
mination of activity periods by all members also 
was frequently rather abrupt. 
This pattern of coincidence of activity shown by 
members of different local colonies is assumed to 
be the basic biological pattern characteristic of 
the species. However, as the total colony increased 
in number through time, there was a gradual alter- 
ation of this pattern to one in which all portions of 
the night were approximately equally utilized. 
This is particularly well in evidence by the last 
period analyzed, Period 10 March and April 
1949 (fig. 90). What this means is that when the 
population was high there was essentially no 
periods during the night when the Food Pen was 
not being utilized to the maximum capacity that 
the rats would tolerate. 
This maximum capacity of utilization of the 
Food Pen was in the order of magnitude of 15 to 
20 rats. This was so whether the colony was small, 
as it was in the fall of 1947, or when it was large as 
in the spring of 1949. Thus, as the colony in- 
creased in size, it was possible for a smaller and 
smaller proportion of the colony to exhibit the 
basic pattern of activity in evidence when the 
colony was small. As the colony increased in size 
more individuals were forced to utilize those periods 
of time left vacant by other rats. As indicated in 
more detail elsewhere in this section on activity, it 
was the socially lower-ranking rats which more 
frequently utilized the predusk and postdawn 
periods, when most other rats were resting in their 
places of harborage. These observations provide 
additional support to the belief that the socially 
low-ranking rats were the ones who altered their 
activity pattern during the night. We may 
schematically represent the situation as shown in 
figure 96. Although this is quite schematic, it 
124 
